Deprecate DefaultSWTFontRegistry and Completely switch to ScalingSWTFontRegistry

    1)Always use ScalingSWTFontRegistry
    2)Rename DefaultSWTFontRegistry -> LegacySWTFontRegistry as this is not default anymore
    3)Add a system property to use LegacySWTFontRegistry without monitor specific scaling active
    3)Deprecate the LegacySWTFontRegistry(DefaultSWTFontRegistry)

Author: arunjose696

bundles/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/internal/DefaultSWTFontRegistryTests.java renamed to bundles/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/internal/LegacySWTFontRegistryTests.java

@@ -23,15 +23,15 @@
 import org.junit.jupiter.api.extension.*;
 
 @ExtendWith(PlatformSpecificExecutionExtension.class)
-class DefaultSWTFontRegistryTests {
+class LegacySWTFontRegistryTests {
 	private static String TEST_FONT = "Helvetica";
 	private Display display;
 	private SWTFontRegistry fontRegistry;
 
 	@BeforeEach
 	public void setUp() {
 		this.display = Display.getDefault();
-		this.fontRegistry = new DefaultSWTFontRegistry(display);
+		this.fontRegistry = new LegacySWTFontRegistry(display);
 	}
 
 	@AfterEach

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/internal/DefaultSWTFontRegistry.java renamed to bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/internal/LegacySWTFontRegistry.java

@@ -19,19 +19,25 @@
 import org.eclipse.swt.internal.win32.*;
 
 /**
- * This class is used in the win32 implementation only to support
- * unscaled fonts in multiple DPI zoom levels.
+ * <p>
+ * Formerly {@code DefaultSWTFontRegistry}, this class is deprecated. Use {@code ScalingSWTFontRegistry} instead.
+ * To temporarily fall back to legacy font behavior ({@code LegacySWTFontRegistry})
+ * (e.g., if issues arise in existing RCP products), set the system property: {@code
+ * -Dswt.fontRegistry=LEGACY
+ * }
+ * </p>
  *
  * As this class is only intended to be used internally via {@code SWTFontProvider},
  * it should neither be instantiated nor referenced in a client application.
  * The behavior can change any time in a future release.
  */
-final class DefaultSWTFontRegistry implements SWTFontRegistry {
+@Deprecated(forRemoval= true, since= "2025-09")
+final class LegacySWTFontRegistry implements SWTFontRegistry {
 	private static FontData KEY_SYSTEM_FONTS = new FontData();
 	private Map<FontData, Font> fontsMap = new HashMap<>();
 	private Device device;
 
-	DefaultSWTFontRegistry(Device device) {
+	LegacySWTFontRegistry(Device device) {
 		this.device = device;
 	}
 

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/internal/SWTFontProvider.java

@@ -105,10 +105,35 @@ public static void disposeFontRegistry(Device device) {
 		}
 	}
 
+	private static enum FontRegistryType {
+		LEGACY, SCALING;
+
+		public static FontRegistryType fromString(String s) {
+			if (s == null) {
+				return SCALING;
+			}
+			for (FontRegistryType type : values()) {
+				if (type.name().equalsIgnoreCase(s)) {
+					return type;
+				}
+			}
+			return SCALING; // fallback to default if invalid
+		}
+	}
+
+	private static final String SWT_FONT_REGISTRY = "swt.fontRegistry";
+	private static final FontRegistryType fontRegistryValue;
+	static {
+		String registryProp = System.getProperty(SWT_FONT_REGISTRY);
+		fontRegistryValue = FontRegistryType.fromString(registryProp);
+	}
+
 	private static SWTFontRegistry newFontRegistry(Device device) {
-		if (device instanceof Display display && display.isRescalingAtRuntime()) {
-			return new ScalingSWTFontRegistry(device);
+		if (fontRegistryValue == FontRegistryType.LEGACY && device instanceof Display display
+				&& !display.isRescalingAtRuntime()) {
+			return new LegacySWTFontRegistry(device);
 		}
-		return new DefaultSWTFontRegistry(device);
+		return new ScalingSWTFontRegistry(device);
+
 	}
 }